Oxidant Concentration Research Articles

A comprehensive evaluation of enhanced temperature influence on gas and aerosol chemistry in the lamp-enclosed oxidation flow reactor (OFR) system

Abstract. Oxidation flow reactors (OFRs) have been extensively utilized to examine the formation of secondary organic aerosol (SOA). However, the UV lamps typically employed to initiate the photochemistry in OFRs can result in an elevated reactor temperature when their implications are not thoroughly evaluated. In this study, we conducted a comprehensive investigation into the temperature distribution within an Aerodyne potential aerosol mass OFR (PAM-OFR) and then examined the subsequent effects on flow and chemistry due to lamp heating. A lamp-induced temperature increase was observed, which was a function of lamp-driving voltage, number of lamps, lamp types, OFR residence time, and positions within the PAM-OFR. Under typical PAM-OFR operational conditions (e.g., < 5 d of equivalent atmospheric OH exposure under low-NOx conditions), the temperature increase typically ranged from 1–5 °C. Under extreme (but less frequently encountered) conditions, the heating could reach up to 15 °C. The influences of the increased temperature over ambient conditions on the flow distribution, gas, and condensed-phase chemistry within PAM-OFR were evaluated. Our findings indicate that the increase in temperature altered the flow field, resulting in a diminished tail on the residence time distribution and corresponding oxidant exposure due to faster recirculation. According to simulation results from a radical chemistry box model, the variation in absolute oxidant concentration within PAM-OFR due to temperature increase was minimal (< 5 %). The temperature influences on seed organic aerosol (OA) and newly formed secondary OA were also investigated, suggesting that an increase in temperature can impact the yield, size, and oxidation levels of representative biogenic and anthropogenic SOA types. Recommendations for temperature-dependent SOA yield corrections and PAM-OFR operating protocols that mitigate lamp-induced temperature enhancement and fluctuations are presented. We recommend blowing air around the reactor's exterior with fans during PAM-OFR experiments to minimize the temperature increase within PAM-OFR. Temperature increases are substantially lower for OFRs utilizing less powerful lamps compared to the Aerodyne version.

Machine learning predict the degradation efficiency of aqueous refractory organic pollutants by ultrasound-based advanced oxidation processes

Ultrasound based advanced oxidation processes (AOPs) are effective for removing refractory organic pollutants by generating reactive species. Machine learning (ML) can systematically provide an excellent opportunity to determine the relationship between feature variables and output variables through large amounts of data, thereby reducing the need for experimental measurements. In this study, a ML approach was applied for the first time to predict the degradation efficiency of aqueous refractory organic pollutants by ultrasound-based AOPs. The obtained dataset was normalized and introduced into four ML models. Among them, Random Forest Regressor and XGB Regressor models had the best fit with 0.9546 and 0.9749 for training set R2 and 0.9548 and 0.9740 for test set R2, respectively. Relative importance analysis and SHAP analysis showed that catalyst type, oxidant concentration, reaction time, and catalyst dosage are the important variables affecting the degradation efficiency of refractory organic pollutants. In addition, excessive ultrasonic intensity, ultrasonic frequency, oxidant concentration, and catalyst dosage had little effect on the increase of degradation efficiency. Based on the descriptive data analysis, high degradation efficiency was obtained with ultrasonic intensity of 2 W·mL−1, ultrasonic frequency of 20–40 kHz, reaction time of 60–90 min, pH 3–7, oxidant concentration of ∼7.5 mmol·L−1, and catalyst dosage of >0.4 g·L−1. This work demonstrated a new predictive method to understand the comprehensive influence of operative factors on degradation efficiency in US-based AOPs, guiding parameter and process optimization.

The application of chromatographic methods in optimization and the enhancement of the oxidative liquefaction process to wind turbine blade recycling

AbstractThe concept of the circular economy aims to maximise the longevity of raw materials, materials, and final goods while simultaneously minimising waste generation. In order to accomplish this objective, researchers are currently exploring emission-free recycling methods and advancing a novel oxidative liquefaction methodology. This process is employed to efficiently degrade the polymer matrix which we can find among other things in wind turbine blades while also conducting chromatographic investigations of the resulting degraded resins. The conducted experiments included a temperature range spanning from 250 °C to 350 °C. The residence lengths varied from 30 to 90 min, while the pressures ranged from 20 to 40 bars. Additionally, the waste-to-liquid ratios were within the range of 5–25%, and the oxidant concentrations were between 15 and 45% by weight. The study’s results will help improve the design of the experiments by focusing on getting the highest concentrations of oxygenated chemical compounds, such as volatile fatty acids, aromatic hydrocarbons, and aromatic carboxylic acids. These compounds are the main chemicals obtained during resin degradation, and identifying the optimal conditions for their production will facilitate the implementation of this process on a larger scale. Graphic abstract

An Electrochemical Phase Field Model Applied to Molten Salt Dealloying Corrosion of Ni-Alloys

Metal alloys in contact with molten salts are known to corrode via a dealloying process, wherein the less-noble alloy elements (e.g. Cr) are selectively oxidized and dissolved, leaving behind a corroded structure that is enriched in the more-noble elements (e.g. Ni). In some cases, this can lead to molten salt infiltration into the alloy through discrete channels along specific microstructural features (e.g. grain boundaries). However, in other cases the dealloying process promotes a more full-scale attack of the alloy, generating a fine-scale ligament structure. This process can severely degrade the alloy’s structural integrity, which limits the practicality of these material systems in otherwise promising applications (e.g. molten salt-cooled power reactors).The thermokinetic conditions for dealloying corrosion depend on the salt chemistry and the metal microstructure, which together inform the reaction process occurring at their interface. The salt chemistry and oxidant content set the electrochemical potential for selective oxidation of the less-noble elements. The associated oxidation rate is expected to depend on the presence of an interfacial structure (e.g. double layer) and also on the transport rates of reactants towards the interface (e.g. species diffusion in the metal and oxidizer transport in the salt) and reaction products away from the interface (cation transport in the salt). The corrosion rate and morphology will also depend strongly on the rate of transport laterally along the metal-salt interface, since the reorganization of the more-noble species (Ni) towards ligament formation facilitates the attack of the alloy by the corrosive agent. It has been hypothesized that molten salts enhance this rate of solute diffusion along the metal interface.In this work, we propose an electrochemical phase field model to predict the microstructural evolution of model Ni-alloys undergoing dealloying corrosion in molten fluoride salts. The model incorporates metal oxidation and dissolution via experimentally determined redox potentials and activity coefficients for metal species in the molten salt. We show that the corrosion rate and development of pores is strongly dependent on solute transport rates within the metal and also along their solid-liquid interface. In particular, we reveal a mechanism in which grain boundaries couple with the solid-liquid corrosion front to promote rapid dealloying and molten salt attack. Oxidant content in the salt and double-layer formation at the interface are discussed for their roles in setting the electrochemical potential and reaction rate at the metal-salt interface. Finally, we discuss how the model leverages insights from atomistic modeling and highlight key knowledge gaps in the mesoscale modeling of electrochemical molten salt corrosion.

(Dielectric Science and Technology Division Poster Award, 3rd Place) Radical Oxidation for Enhancing Polishing-Rate and Improving Slurry Stability in Ag-Film Chemical–Mechanical-Planarization

Recently, Ag-film has been utilized as a reflective layer in organic-light-emitting- diode on silicion(OLEDoS). The formation of a reflective Ag-film layer was conducted by Ag-film deposition and following Ag-film chemical-mechanical planarization (CMP). The Ag-film has ductility property (i.e., hardness of 0.3 GPa) so that a reletively soft CMP pad should be used to minimize the generation of the CMP induced scratches. However, using a soft CMP pad, it is notably difficult to achieve a high Ag-film polishing-rate (i.e., 300 nm/min). Thus, to enhance Ag-film polishing-rate, a Fenton reaction between ferric ions and H2O2 has been applied. Although, a Fenton reaction enhancing dissolved oxygen concentration can increase remarkably the Ag-film polishing-rate, the CMP slurry using Fenton reaction has produced a detrimental slurry stability after mixing with H2O2 (i.e., extremely low H2O2 pot life time. In this study, as a solution, the Ag-film CMP slurry was designed via radical oxidation on the Ag-film surface during CMP, without using Fenton reaction (i.e., mixing ferric ions with H2O2). The radical oxidation was achived by using halide oxidant (i.e., H5IO6), which radical oxidation degree principally depended on halide oxidant concentration and slurry pH, showing a notable high Ag-film polishing-rate (i.e., 400 nm/min) without the precence of corrosion. Without using Fenton reaction, the secondary diameter of colloidal abrasives in the designed Ag-film CMP slurry was not changed for several months. In our presentation, we will prove the mechanism of the radical oxidation on the polished Ag-film surface. In addition, we will present the dependencies of the chemical dominant polishing properties (i.e., OH radical, chemical oxidation degree of the Ag-film surfcae, chemical composition of chemical oxidation, slurry adsortion degree, and corrosion potential and current) as well as the mechanical dominant polishing properties (i.e., electrostatic force between abrasives and Ag-film surface) on the halid oxidant concentration.

Cascading sulfur cycling in simulated oil sands pit lake water cap mesocosms transitioning from oxic to euxinic conditions

Base Mine Lake (BML), the first full-scale demonstration of oil sands tailings pit lake reclamation technology, is experiencing expansive, episodic hypolimnetic euxinia resulting in greater sulfur biogeochemical cycling within the water cap. Here, Fluid Fine Tailings (FFT)-water mesocosm experiments simulating the in situ BML summer hypolimnetic oxic-euxinic transition determined sulfur biogeochemical processes and their controlling factors. While mesocosm water caps without FFT amendments experienced limited geochemical and microbial changes during the experimental period, FFT-amended mesocosm water caps evidenced three successive stages of S speciation in ∼30 days: (S1) rising expansion of water cap euxinia from FFT to water surface; enabling (S2) rapid sulfate (SO42−) reduction and sulfide production directly within the water column; fostering (S3) generation and subsequent consumption of sulfur oxidation intermediate compounds (SOI). Identified key SOI, elemental S and thiosulfate, support subsequent SOI oxidation, reduction, and/or disproportionation processes in the system. Dominant water cap microbes shifted from methanotrophs and denitrifying/iron-reducing bacteria to functionally versatile sulfur-reducing bacteria (SRB) comprising sulfate-reducing bacteria (Desulfovibrionales) and SOI-reducing/disproportionating bacteria (Campylobacterales and Desulfobulbales). The observed microbial shift is driven by decreasing [SO42−] and organic aromaticity, with putative hydrocarbon-degrading bacteria providing electron donors for SRB. Comparison between unsterile and sterile water treatments further underscores the biogeochemical readiness of the in situ water cap to enhance oxidant depletion, euxinia expansion and establishment of water cap SRB communities aided by FFT migration of anaerobes. Results here identify the collective influence of FFT and water cap microbial communities on water cap euxinia expansion associated with sequential S reactions that are controlled by concentrations of oxidants, labile organic substrates and S species. This emphasizes the necessity of understanding this complex S cycling in assessing BML water cap O2 persistence.

Hypersensitivity to man-made electromagnetic fields (EHS) correlates with immune responsivity to oxidative stress: a case report

ABSTRACT There is increasing evidence that exposure to weak electromagnetic fields (EMFs) generated by modern telecommunications or household appliances has physiological consequences, including reports of electromagnetic field hypersensitivity (EHS) leading to adverse health effects. Although symptoms can be serious, no underlying mechanism for EHS is known and there is no general cure or effective therapy. Here, we present the case study of a self-reported EHS patient whose symptoms include severe headaches, generalized fatigue, cardiac arrhythmia, attention and memory deficit, and generalized systemic pain within minutes of exposure to telecommunications (Wifi, cellular phones), high tension lines and electronic devices. Tests for cerebral, cardiovascular, and other physiological anomalies proved negative, as did serological tests for inflammation, allergies, infections, auto-immune conditions, and hormonal imbalance. However, further investigation revealed deficits in cellular anti-oxidants and increased radical scavenging enzymes, indicative of systemic oxidative stress. Significantly, there was a large increase in circulating antibodies for oxidized Low-Density Lipoprotein (LDLox), byproducts of oxidative stress accumulating in membranes of vascular cells. Because a known primary effect of EMF exposure is to increase the concentration of cellular oxidants, we propose that pathology in this patient may be causally related to a resulting increase in LDLox synthesis. This in turn could trigger an exaggerated auto-immune response consistent with EHS symptoms. This case report thereby provides a testable mechanistic framework for EHS pathology with therapeutic implications for this debilitating and poorly understood condition.

Oxidant concentrations and photochemistry in a vehicle cabin.

Indoor air quality (IAQ) in vehicles can be important to people's health, especially for those whose occupations require them to spend extensive time in vehicles. To date, research on vehicle IAQ has primarily focused on direct emissions as opposed to chemistry happening in vehicle cabins. In this work, we conducted time-resolved measurements of the oxidants and oxidant precursors ozone (O3), nitric oxide (NO), nitrogen dioxide (NO2), and nitrous acid (HONO) inside the cabin of a 2012 Toyota Rav4 under varying ventilation conditions (i.e., car off, car on with passive ventilation, car on with mechanical ventilation via the recirculating fan, and car on with mechanical ventilation via the direct fan). Ozone levels inside the vehicle were significantly lower than outdoors under most conditions, and were approximately half the outdoor levels when the direct fan was in operation. Nitric oxide and NO2 concentrations were very low both inside the vehicle and outdoors. Nitrous acid levels in the vehicle were lower than reported values in other indoor environments, though much higher than expected outdoor levels. We also investigated the potential for photochemical production of radicals in the vehicle. Time- and wavelength-resolved solar irradiance spectra were collected, and steady state hydroxyl radical (OH) and nitrate radical (NO3) concentrations were calculated. Steady state OH concentrations were predicted to be similar to those in air masses in residences illuminated by sunlight, suggesting the importance of HONO photolysis in vehicles. Conversely, nitrate radicals (NO3) were not considered significant indoor oxidants in our study due to rapid titration by NO. Overall, our findings emphasize the importance of both air exchange and photochemistry in shaping the composition of air inside vehicles.

Comparative study of Fe(III)/peroxymonosulfate, Fe(III)/hydrogen peroxide and Fe(III)/peroxydisulfate systems modified by sinapic acid for micropollutants degradation

Sinapic acid (SA) as an environmentally friendly natural phenolic acid, has the properties of antioxidant because of containing –OH and –OCH3 on the benzene ring and it is safe. The Fe(III)/peroxymonosulfate (PMS) system modified by SA for enhancing micropollutant degradation had been studied, while weather SA could improve micropollutant degradation in other Fe(III)/oxidants systems was still unclear. The Fe(III)/hydrogen peroxide (H2O2) and Fe(III)/peroxydisulfate (PDS) systems modified by SA for micropollutants degradation were studied, the results indicated that SA could enhancing micropollutants degradation by accelerating the Fe(III)/Fe(II) cycle in both systems. In addition, the PMS, the H2O2 and the PDS systems were compared, and ten micropollutants commonly present in natural water were selected to evaluate the oxidation capacity of different systems. The PMS and PDS systems have higher oxidation degradation capacity for ten micropollutants than that of H2O2 system, attributed to the SO4•−, HO• and Fe(IV) all contributing to micropollutants degradation. However, in the H2O2 system, ten micropollutants degradation almost entirely relied on HO•. In the PMS and PDS systems, the SO4•− played a dominated role for micropollutants removal, attributed to its higher steady-state concentration than HO• and its higher second-order reaction rate with micropollutants than Fe(IV). Economic evaluation indicted that the H2O2 system was more cost-effective than the PMS and PDS systems for micropollutants removal. This was because the cost of H2O2 was lower than PMS and PDS, and concentration of Fe(III), oxidants and SA requirements in the H2O2 system were lower than that in the PMS and PDS systems. Overall, this study provided an economical and environmental-friendly method for the efficient treatment of harmful micropollutants in wastewater.

Degradation of bromothymol blue and methyl green from aqueous media by Photo-Fenton: comparison between UV-lamp and sun irradiation

Abstract The degradation of two textile dye molecules was studied using photochemical processes, both in the absence and presence of light. Various methods were employed, including photolysis/UV, combined H2O2/UV photolysis, Fe2+/UV treatment, Photo-Fenton/UV at 350 nm and Photo-Fenton with solar irradiation. The decolorization efficiency of dyes in aqueous solution was evaluated for two specific dyes: Bromothymol Blue (BTB) and Methyl Green (MG). These experiments were carried out in batch mode. The results demonstrated a synergy between light irradiation and the presence of Fenton’s reagents, such as hydrogen peroxide and divalent iron. In addition, it was demonstrated that direct solar irradiation can be used without specific devices to achieve high efficiency at low cost. In the first part, we checked the impact of the various operating parameters. Reaction efficiencies were compared for the same system in the dark and under the assistance of an artificial or solar light source. In the second part, we studied the parameters of the Photo-Fenton process, such as the initial pH of the solution, the initial concentrations of oxidant, iron catalyst, and dye under irradiation from either light source. Whereas the mere photolysis without Fenton’s reagents allowed decolorization yields below 26 %, addition of the oxidant (H2O2) or the catalyst (Fe(II) species amplified the treatment efficiency. However, the presence of both H2O2 and Fe(II) under light irradiation was shown synergetic with yields ranging from 72 to 85 % depending on the dye worked and the light source: because of its broader spectrum in the UV domain, solar irradiation led to the highest decolorization yields. The above results were obtained for well-defined proportions of dye and reagents: for a 20 mg/l dye solution, Fe(II) catalyst concentration equal to 10−3 M, peroxide concentration of 5.10−2 M and a pH of 3. These conditions allowed optimal production of OH· radicals, allowing high efficiency in systems using solar irradiation.

Optimizing Glyphosate Removal from Water Using a Peracetic Acid-Assisted Advanced Oxidation Process: A Response Surface Methodology Approach

Glyphosate (GLY), one of the most used pesticides in the world, has been frequently detected in water, posing chronic and remote hazards to human health and the environment. Consequently, it has become necessary to develop efficient and sustainable treatment processes able to remove GLY from the polluted aquatic environments. In this context, the use of advanced oxidation processes is of great interest, as it allows for a significant reduction in concentrations of recalcitrant pollutants. In this study, peracetic acid (PAA) was used for the first time to remove GLY from water. In particular, the process parameters (oxidant dose, activation by UV radiation, GLY concentration, process time) were optimized using central composite design (CCD) and response surface methodology (RSM). The degradation of the pollutant, i.e., GLY, was monitored by ion chromatography, optimizing the instrumental parameters. During the process, residual oxidant concentrations were also constantly monitored using reference methods (i.e., UV-visible spectroscopy). Based on the results obtained, the best GLY removals (over 90%) were achieved under the following conditions: a PAA/GLY molar ratio of 3 (concentration of 3.0 mg/L for GLY and 4.0 mg/L for PAA), UV irradiation, and a process time of 45 min. The possibility of achieving total glyphosate removal by using small amounts of oxidant increases the environmental sustainability of the proposed aquatic pollution mitigation strategy.

Investigating the efficiency of Photo-Fenton (UV/H2O2/Fe2+) in removing the indomethacin antibiotic from aqueous solutions

Water pollution caused by antibiotics is one of the major challenges in the world today. The current research aims to investigate the effect of the Photo-Fenton process in removing indomethacin antibiotics from aqueous solutions. This experiment-based study was conducted on a laboratory scale and discontinuous manner. The influential variables affecting the removal efficiency of indomethacin include initial antibiotic concentration, pH, time, hydrogen peroxide concentration, and iron ion. The study was conducted base on standard methods (APHA, AWWA, CFWP, 2005). The Design Expert software was used to analyze the effect of independent variables on the removal efficiency of indomethacin antibiotics in the Photo-Fenton process (UV/H2O2/Fe2+) using response surface methodology (RSM) and central composite design (CCD). To ensure the repeatability of the results, each experiment was repeated three times and the reported the average. The results showed that the optimal removal conditions for indomethacin antibiotics were pH = 4, H2O2 oxidant concentration = 50 ppm, Fe2+catalyst concentration = 50 ppm, time = 75 minutes, and initial antibiotic concentration = 20 ppm, with a removal efficiency of 91.03%. The variables of initial antibiotic concentration, H2O2 concentration, and pH had the greatest impact on the removal efficiency of indomethacin. The results of this study indicate that under optimal conditions, more than 90% of indomethacin antibiotics can be removed from aqueous solutions using the Photo-Fenton process, which is a significant result for removing this pharmaceutical pollutant from aquatic environments.

Remediation of phenanthrene contaminated soil by persulphate coupled with Pseudomonas aeruginosa GZ7 based on oxidation prediction model.

Chemical oxidation coupled with microbial remediation has attracted widespread attention for the removal of polycyclic aromatic hydrocarbons (PAHs). Among them, the precise evaluation of the feasible oxidant concentration of PAH-contaminated soil is the key to achieving the goal of soil functional ecological remediation. In this study, phenanthrene (PHE) was used as the target pollutant, and Fe2+-activated persulphate (PS) was used to remediate four types of soils. Linear regression analysis identified the following important factors influencing remediation: PS dosage and soil PHE content for PHE degradation, Fe2+ dosage, hydrolysable nitrogen (HN), and available phosphorus for PS decomposition. A comprehensive model of "soil characteristics-oxidation conditions-remediation effect" with a high predictive accuracy was constructed. Based on model identification, Pseudomonas aeruginosa GZ7, which had high PAHs degrading ability after domestication, was further applied to coupling repair remediation. The results showed that the optimal PS dose was 0.75% (w/w). The response relationship between soil physical, chemical, and biological indicators at the intermediate interface and oxidation conditions was analysed. Coupled remediation effects were clarified using microbial diversity sequencing. The introduction of Pseudomonas aeruginosa GZ7 stimulated the relative abundance of Cohnella, Enterobacter, Paenibacillus, and Bacillus, which can promote material metabolism and energy transformation during remediation.

The effect of exogenous melatonin administration before superovulation on embryo yield in Assaf ewes.

The aim of this study was to determine the effect of exogenous melatonin administration on transferable embryos by increasing total antioxidant status before superovulation in Assaf ewes. Selected ewes were randomly divided into two equal groups: melatonin (n = 9) and control (n = 9). In the melatonin group, a melatonin implant (18 mg melatonin, Regulin®, Ceva, Turkey) was placed under the skin of the ear 7 days prior to insertion of the progesterone-containing sponge. In the control group, a physiological saline solution was injected under the skin of the ear on the same day. The same superovulation protocol was used in both groups. In addition, blood samples for determination of Glutathione peroxidase, superoxide dismutase, total antioxidant status and total oxidant status concentrations were collected on five different days, including the day of melatonin implant placement (Day-7), vaginal sponge insertion (Day 0), vaginal sponge removal (Day 11), mating (Day 12-13) and uterine flushing (Day 19). Embryos were collected by laparotomy on the 7th day after mating. Uterine flushing taken into petri dishes were scanned under a stereomicroscope, and the quality and developmental stages of the embryos were recorded. In the study, total corpus luteum count and total cell count were found to be higher in the control group than in the melatonin group (p < .05). When the results were evaluated in terms of oxidative stress index, a negative correlation was found between the total number of corpus luteum, number of cells obtained, count of transferable embryos and number of Grade 1 embryos on Day 0. There was also a positive correlation oxidative stress index and the number of unfertilized oocytes on Day-7. As a result, exogenous melatonin administration prior to superovulation during the breeding season is thought to have a negative effect on embryo yield and quality. Therefore, the use of exogenous melatonin in MOET studies during the breeding season is recommended to be investigated in new studies.

The PCSK9 Protein Is Not Necessarily a Risk Factor for Major Depressive Disorder.

Major depressive disorder (MDD) is one of the common psychiatric disorders that is characterized by abnormal neurobiological responses. Proprotein convertase subtilisin/kexin 9 (PCSK9) is important in cholesterol homeostasis. This study aimed to investigate PCSK9 levels and oxidative stress with MDD disease. The study included 30 patients with MDD and 30 healthy controls. Their blood samples were collected in sterile tubes, and the serum PCSK9 concentration, superoxide dismutase (SOD), and glutathione peroxidase (GPx) activity were determined by ELISA kits. Total antioxidant capacity (TAC), total oxidant status (TOS), malondialdehyde (MDA), and copper concentration were determined manually. There was a significant increase in PCSK9 levels in the patient group (P<0.05). The receiver operating characteristic (ROC) curve with a sensitivity of 57% and specificity of 52% was 0.928 (95% CI, 0.86-0.996) for PCSK9 in the patient group (P<0.001). It was found that MDA (P=0.036) level was higher in the MDD group, but TAC (P=0.445) level, SOD (P=0.148), GPx (P=0.019) activities, and copper concentration were lower in the patient group compared with the control group. The study results confirm the relationship between oxidative stress and MDD and also suggest a link between PCSK9 and MDD disease.

Sustained release and self activation of peroxydisulfate intercalated Ca/Al-layered double hydroxide in the remediation of organic contaminated soil

To keep the sufficient effective concentration of oxidants during the in-situ chemical oxidation (ISCO) for organic polluted soil, peroxydisulfate (S2O82−, PDS) intercalated Ca/Al-layered double hydroxide (LDH) was employed as sustainable released and self-activated material of PDS. In the simulated diesel contaminated soil (1000 mg/kg) column with Ca/Al-PDS LDH dosage of 1 wt% and a water flow rate of 0.2 mL/min, PDS released sustained around 50 d, and the final removal rate of diesel could reach 70%, which mainly attributed to Ca/Al-PDS LDH for the oxidation decomposition of diesel. A coupled mechanism between PDS release from Ca/Al PDS LDH and organics oxidation process was proposed according to the concentration of Ca2+ and Al3+ in solution and the X-ray diffraction (XRD) analysis of the solid residue. The generated organic acids and SO42− after the oxidation promoted the dissolution of LDH layers and ion exchange of PDS with SO42− respectively, thereby enhancing the release of PDS. The result of electron paramagnetic resonance (EPR) showed that the oxidative species (•OH, SO4−• and 1O2) were generated both in the reaction solution and on LDH, resulting from the activation of PDS by the aqueous OH− and the Lewis basicity on Ca/Al-PDS LDH, respectively. Thus the oxidation process occurred both in the homogeneous and heterogeneous pattern. This study provided a novel design strategy of sustained-released and self-activated oxidants for the remediation of organic contaminated soil.

UV/Advanced Oxidation Process for Removing Humic Acid from Natural Water: Comparison of Different Methods and Effect of External Factors

Humic acid (HA) is an organic compound naturally present in aquatic environments. It has been found to have detrimental effects on water color, the transport of heavy metals, and the elimination of disinfection by-products (DBPs), thereby exerting an impact on human health. This study introduced four synergistic ultraviolet/advanced oxidation processes (UV/AOPs) systems aimed at eliminating HA from water. The research explored the effect of solution pH, duration of illumination, initial reactant concentration, and oxidant concentration on the degradation of HA. The results indicated that the mineralization rate achieved by individual UV or oxidant systems was less than 15%, which is significantly lower compared to UV/AOPs systems. Among these methods, the UV/peroxymonosulfate (UV/PMS) process demonstrated the highest effectiveness, achieving a mineralization rate of 94.15%. UV/peroxydisulfate (UV/PDS) and UV/sodium percarbonate (SPC) were subsequently implemented, with UV/sulfite (S(IV)) demonstrating the lowest effectiveness at 19.8%. Optimal degradation efficiency was achieved when the initial concentration of HA was 10 mg/L, the concentration of PMS was 3 mmol/L, and the initial pH was set at 5, with an illumination time of 180 min. This experimental setup resulted in high degradation efficiencies for chemical oxygen demand (COD), UV254, and HA, reaching 96.32%, 97.34%, and 92.09%, respectively. The energy efficiency of this process (EE/O) was measured at 0.0149 (kWh)/m3, indicating the capability of the UV/PMS system to efficiently degrade and mineralize HA in water. This offers theoretical guidance for the engineered implementation of a UV/PAM process in the treatment of HA.

Degradation of Dyes Catalyzed by Aminophenyl-Substituted Mn-Porphyrin Immobilized on Chloropropyl Silica Gel and Evaluation of Phytotoxicity.

A heterogenized Mn(III) porphyrin-based catalyst was prepared for dye degradation. The new Mn(III) complex of 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin was immobilized, via covalent bond, in chloropropyl silica gel, generating the material (Sil-Cl@MnP) with a loading of 23 μmol manganese porphyrin (MnP) per gram of Sil-Cl. This material was used as a catalyst in degradation reactions of model dyes, a cationic dye [methylene blue (MB)] and an anionic dye (reactive red 120, RR120), using PhI(OAc)2 and H2O2 as oxidants. The oxidation reactions were carried out after the dye reached adsorption/desorption equilibrium with the catalytic material, with a much higher percentage of adsorption being observed for the cationic MB dye (20%) than for the anionic RR120 dye (3%), which may be associated with electrostatic attraction or repulsion effects, respectively, with the negatively charged surface of the silica (zeta potential measurement for Sil-Cl@MnP, ζ = -19.2 mV). In general, there was a higher degradation percentage for MB than for RR120, probably because the size and charge of RR120 would hinder its approach to the MnP active species on the silica surface. With respect to the oxidant, the PhI(OAc)2-based systems showed a higher degradation percentage than those of H2O2. It was observed that the increase in the oxidant concentration promoted a significant increase in the degradation of MB, with a degradation of approximately 65%. The efficiency of the catalyst was also evaluated after successive additions of the oxidant every 2 h, and it can be seen that the catalyst had no loss of efficiency, with a degradation percentage greater than 80% being observed after 8 h of reaction. The phytotoxicity of the products formed in the system was evaluated in a 1:23.5:188 molar ratio Sil-Cl@MnP: MB:PhI(OAc)2 was used. In these studies, phytotoxicity was found for the germination of lettuce seeds when the original solution was used without dilution; however, when diluted (10% V/V), the results were close to the positive and negative controls. Thus, the material obtained proved to be a potential candidate for application in the degradation reactions of environmental pollutants.

Modification of morphological, structural and optical properties of graphene oxide by alteration molarity of aqueous KMnO4 solution

This work reports a nontraditional modified Hummer’s method to synthesize graphene oxide (GO) nanosheets by adjusting the oxidation process via a different-molarity potassium permanganate (KMnO4) solution instead of utilizing its powder. The effect of KMnO4 concentrations on the structural and morphological properties of GO nanosheets was studied. Oxidant solutions of 0.5 M, 1 M and 1.5 M were experimented to control the properties of the GO layers. Then, the samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), Raman and ultraviolet-visible (UV–Vis) spectroscopes. Finally, oxidant concentration was optimized at 1 M by which thinner, high-quality crystalline GO layers and wider bandgap energy ( E g ) were obtained. It is thus confirmed that such a modification in the oxidation is a pioneering process to improve the GO properties.

Advancing PFAS characterization: Development and optimization of a UV-H2O2-TOP assay for improved PFCA chain length preservation and organic matter tolerance

As per- and polyfluoroalkyl substances (PFAS) infiltrate the environment via industrial, commercial, and domestic sources, the demand for robust, cost-effective, and straightforward analytical assays intensifies to enhance PFAS characterization and quantification. To address this demand, this study introduces a novel UV-H2O2-TOP assay, identifying optimal parameters such as pH (5–9), oxidant concentration (500 mM H2O2), activation rate (63 mM H2O2 h−1), and an acceptable total organic carbon (TOC) limit (~1000 mg/L TOC) to achieve maximum PFAA precursor conversion. Additional work was performed further optimizing the UV-TOP assay, by confirming its superiority to heat activation, identifying the effectiveness of different persulfate salts, and investigating different concentrations of sodium persulfate and sodium hydroxide at a 1:2.5 ratio on PFCA yield. Our investigation concluded by applying the UV-H2O2-TOP assay, using sodium persulfate as the TOP assay oxidant, to 6:2 FTS and five different AFFF samples. High-resolution mass spectrometry and an expanded analytical suite support sample analysis, facilitating direct quantification of ultra-short chain perfluoroalkyl carboxylates (PFCAs) and common fluorotelomer compounds including 5:3/5:1:2 fluorotelomer betaine and 6:2 fluorotelomer sulfonamido betaine. Results highlight several advantages of this tandem UV-activated method, including enhanced preservation of perfluoroalkyl chains (post-oxidation of 6:2 fluorotelomer sulfonate resulted in 28 % PFHpA, 47 % PFHxA, 25 % C3–C5 PFCA), capacity to handle high TOC limits (1000 mg/L TOC), and ability to incorporate higher persulfate concentrations in a single oxidation cycle.